Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session Y2: Kondo Physics and Spin Control in Nanostructure Optics and Transport |
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Sponsoring Units: DCMP Chair: Mikhail Raikh, University of Utah Room: LACC 151 |
Friday, March 25, 2005 11:15AM - 11:51AM |
Y2.00001: Kondo effect in a many-electron quantum ring Invited Speaker: The Kondo effect is investigated in a many-electron quantum ring as a function of magnetic field. For fields applied perpendicular to the plane of the ring a modulation of the Kondo effect with the Aharonov-Bohm period is observed. This effect is discussed in terms of the energy spectrum of the ring and the parametrically changing tunnel coupling. In addition, we use gate voltages to modify the ground state spin of the ring. The observed splitting of the Kondo related zero bias anomaly in this configuration is tuned with an in-plane magnetic field. It has been shown that the dot-lead coupling can be determined quantitatively for quantum dots connected to three terminals. The Kondo effect is studied in a three-terminal quantum ring. By measuring the currents through the differently biased terminals it can be determined which lead has Kondo correlations with the dot and which does not. The possibility to probe the density of the dot in the Kondo regime using a three-terminal configuration is discussed. This work was done in collaboration with A. Fuhrer, R. Leturcq, and T. Ihn. A. Fuhrer, et al., Phys. Rev. Lett. 93, 176803 (2004), cond-mat/0406247 [Preview Abstract] |
Friday, March 25, 2005 11:51AM - 12:27PM |
Y2.00002: Transport Spectroscopy of Coupled Quantum Dots in Conditions of the Kondo Effect Invited Speaker: We develop electron transport theory for novel devices [1,2], which are interesting in the context of correlated electrons physics. The device proposed in Ref. [1] is designed for an observation of a non-Fermi-liquid behavior of itinerant electrons. The device measured in Ref. [2] may serve a similar purpose, and also may become important for quantum computing.\\ In the case of Ref. [1], our theory [3] provides a strategy for tuning to the non-Fermi-liquid fixed point -- a quantum critical point in the space of device parameters. We explore the corresponding quantum phase transition, and make explicit predictions for the behavior of differential conductance in the vicinity of the quantum critical point. \\ Motivated by the measurements [2], we developed a theory of conductance of Kondo quantum dots coupled by the RKKY interaction [4]. Investigation of the differential conductance at fixed interaction strength may allow one to distinguish between the possible ground states of the system. Transition between the ground states is achieved by tuning the interaction strength; the nature of the transition (which includes a possibility of a non-Fermi-liquid point) can be extracted from the temperature dependence of the linear conductance.\\ This research is supported by NSF grants DMR02-37296 and EIA02- 10736.\\ 1. Y. Oreg and D. Goldhaber-Gordon, Phys. Rev. Lett. {\bf 90}, p. 136602 (2003). \\ 2. N.J. Craig J.M. Taylor, E.A. Lester, C.M. Marcus, M.P. Hanson, and A.C. Gossard, Science {\bf 304}, 565 (2004).\\ 3. M.G. Vavilov and L.I. Glazman, preprint cond-mat/0404366.\\ 4. M. Pustilnik, L. Borda, L.I. Glazman, and J. von Delft, Phys. Rev. {\bf B 69}, 115316 (2004). [Preview Abstract] |
Friday, March 25, 2005 12:27PM - 1:03PM |
Y2.00003: Electrical control of the spin-flip rate of an exciton in a semiconductor Invited Speaker: At the heart of the Kondo effect is a tunneling process in which a localised electron is exchanged with an electron in a Fermi sea. This process can flip the spin of the localised electron. We present here a novel application of this concept to an exciton, an electron-hole complex, in a quantum dot. By determining the temporal emission characteristics of a single self-assembled quantum dot, we show that the exciton spin can be reversed through an electron exchange with a Fermi sea in a neighboring n-doped layer. A very significant point is that the exciton spin flip completely changes the radiative properties of the exciton, either from dark to bright or from bright to dark. We can control the rate of the spin flip to be either much larger or much smaller than the radiative recombination rate of the bright exction simply with the voltage applied to the gate of our device. Calculations based on the Anderson Hamiltonian give excellent agreement with the experimental results. Our work has important consequences in two areas. First, the effect corresponds to the high temperature Kondo regime, motivating the possibility of observing a Kondo exciton in a semiconductor nanostructure for the first time. Secondly, the effect offers a way of manipulating the dark exciton and therefore a means of exploiting its long lifetime and long spin coherence time in quantum information processing. [Preview Abstract] |
Friday, March 25, 2005 1:03PM - 1:39PM |
Y2.00004: Kondo Effect and Controlled Spin-Entanglement in Coupled Quantum Dots Invited Speaker: Semiconductor double-quantum dots represent an ideal system for studying the novel spin physics of localized spins. On each quantum dot when the number of electrons is odd and the net spin is 1/2, a strong coupling of this localized spin to conducting electrons in the leads gives rise to Kondo correlation. On the other hand, in the coupled double-quantum-dot if the inter-dot antiferromagnetic interaction is strong, the two spins can form a correlated spin-singlet state, quenching the Kondo effect. This competition between Kondo and antiferromagnetic correlation is studied in a controlled manner by tuning the inter-dot tunnel coupling. Increasing the inter-dot tunneling, we observe a continuous transition from a single-peaked to a double-peaked Kondo resonance in the differential conductance. On the double-peaked side, the differential conductance becomes suppressed at zero source-drain bias. The observed strong suppression of the differential conductance at zero bias provides direct evidence signaling the formation of an entangled spin-singlet state. This evidence for entanglement and the tunability of our devices bode well for quantum computation applications. [Preview Abstract] |
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